Thermally stable, high surface area (e.g., &gt;100 m2/g) alumina in the form of small beads or as micron-sized washcoat particles has long been used as a carrier for finely dispersed particles of noble metals in the treatment of automobile exhaust. More recently, ceric oxide (CeO.sub.2, also called ceria) has been incorporated into the alumina particles or mixed with them as the carrier for the dispersed particles of platinum and/or palladium and rhodium. Initially, ceria was used in small amounts, about 2 to 3 percent by weight of the alumina. Now it is being used in larger proportion of the alumina, about 20 to 40 percent by weight of the carrier. It is now necessary to give attention to how to best utilize the ceria from the standpoint of catalyst cost and performance.
Accordingly, it is an object of our invention to provide an improved method of preparing an alumina-ceria catalyst support for the treatment of automotive engine exhaust gases.
It is a more specific object of our invention to provide a method of forming a high surface area ceria for combination with alumina as a catalyst carrier washcoat on a monolithic-type catalyst substrate. The resultant washcoat improved catalyst durability as reflected in the high conversion of HC, CO and NOx even after prolonged thermal aging of the catalyst.
It is another object of our invention to provide a more durable alumina-ceria catalyst carrier washcoat for ceramic or metallic monolith-type catalyst substrates.